Choline levels in plasma will be measured in uremic humans undergoing chronic maintenance hemodialysis. The clearance of choline into the dialysate will be measured. The ability of the organism to regulate the plasma choline levels homeostatically in the face of the loss due to hemodialysis will be observed. Such responses will be analyzed in relation to the toxic effects of uremia and hemodialysis, particularly on the nervous system. Choline clearances during hemodialysis will be observed similarly in dogs. The effects of drugs on this homeostatic regulation will be assessed. The ability of chicken kidneys to metabolize trimethylamine to trimethylamine oxide will be confirmed and extended in in vitro studies. The renal N-oxidation of a number of drugs will be measured.